The pharmacological function and importance of calcium antagonists, or calcium channel blockers, is well known and has been extensively reported in the literature [see; e.g., P. D. Henry, "Comparative Pharmacology of Calcium Antagonists: Nifedipine, Verapamil and Diltiazem", The American Journal of Cardiology, 46, 1047-1058 (1980); K. H. Dangman, et al., "Effects of Nifedipine on Electrical Activity of Cardiac Cells", The American Journal of Cardiology, 46, 1061-1067 (1980); E. Braunwald, "Introduction: Calcium Channel Blockers", "The American Journal of Cardiology, 46, 1045 (1980); L. D. Hillis, "The New Coronary Vasodilators: Calcium Blockers", J. Card. Med., 5(6), 583 (1980); M. J. Berridge, "Receptors and Calcium Signalling", Trends in Pharmacological Sciences 1, 419, (1980); W. G. Nayler, et al., "Calcium Antagonists: definition and mode of action", Basic Research in Cardiology, 76, No. 1, 1-15 (1981)].
Dihydropyridines have been employed to prepare dihydroazepines. For example, Anderson, et al. [J. Chem. Soc., 2411 (1965)] disclose solvolysis of esters of dihydropyridines to obtain alkoxy dihydroazepines, and Turchi, et al. [J. Heterocyclic Chem., 17, 1593-95 (1980)] disclose the preparation of 4,5-dihydroazepines via mesoionic oxazolium 5-oxides by heating primary or secondary .alpha.-amino acids in acetic anhydride in the presence of 1,2-dicyanocyclobutene.